Device for fastening the inner end of a mainspring to the barrel arbor of a clockwork

ABSTRACT

Means for fastening the inner end of a mainspring to the barrel arbor of watch movements, clock movements, etc., in which the end of the mainspring is wound in at least two turns on the smooth cylindrical surface of the barrel arbor. In order that the two turns be in contact with the arbor, the mainspring is cut in the shape of an isosceles triangle at its end and has a triangular opening having two sides parallel to the edges of the blade of the mainspring and a base. The proportions selected permit the winding of the tip of the mainspring on the arbor. As a variant, the mainspring could also be cut with a tongue having oblique parallel edges.

United States Patent [191 Giger DEVICE FOR FASTENING THE INNER END OF A MAINSPRING TO THE BARREL ARBOR OF A CLOCKWORK [75] Inventor: Urs Gige r, Solothurn, Switzerland [73] Assignee: ETA A. G. Erbauches-Fabrik,

Grenchen (Soleure), Switzerland 22 Filed: Jan. 15,1974 21 Appl.No.:433,479

[30] Foreign Application Priority Data Feb. 9, 1973 Switzerland 1905/73 [52] US. Cl. 58/87 [51] Int. Cl. G04b 1/18 [58] Field of Search 58/86, 87; 59/92 [56] References Cited FOREIGN PATENTS OR APPLICATIONS 612,146 9/1934 Germany 58/87 [111 3,834,154 [451 Sept. 10,1974

Primary Examiner-George H. Miller, Jr. Attorney, Agent, or Firm- Stevens, Davis, Miller & Mosher [57] ABSTRACT Means for fastening the inner end of a mainspring to the barrel arbor of watch movements, clock movements, etc., in which the end of the mainspring is wound in at least two turns on the smooth cylindrical surface of the barrel arbor. In order that the two turns be in contact with the arbor, the mainspring is cut in the shape of an isosceles triangle at its end and has a triangular opening having two sides parallel to the edges of the blade of the mainspring and a base. The proportions selected permit the winding of the tip of the mainspring on the arbor. As a variant, the mainspring could also be cut with a tongue having oblique parallel edges.

5 Claims, 6 Drawing Figures DEVICE FOR FASTENING THE INNER END OF A MAINSPRING TO THE BARREL ARBOR OF A CLOCKWORK BACKGROUND OF THE INVENTION The barrel arbors used up to the present time in clockworks and more particularly in watch movements, contain in their central portion located in the center of the barrel an element of cylindrical surface from which there protrudes a hook intended to retain the inner end of the mainspring. This hooking permits the cocking of the spring when the arbor is driven in rotation by the ratchet wheel and the holding fast of its inner end during the normal operation of the movement, while the ratchet wheel is held fast by the holding click. The manufacture of the customary arbors therefore requires milling operations which increase the time of production and the cost of these parts. These customary fastening devices also require a hole to be made at the end of the mainspring.

The object of the present invention is to simplify the manufacture of barrel'arbors by creating a device for fastening the inner end of the mainspring to the arbor which no longer requires any milling on the barrel arbor.

The invention is based on the finding that by cutting the end of the spring in such a manner that it rests against a surface of revolution of the arbor over a length equal to at least two turns, the friction between the arbor and the spring and the elastic clamping resulting from the fact that the inner turns are wound upon manufacture at a diameter which is less than that of the arbor were sufficient to assure a fastening which satisties the requirements established.

Its object is a device for fastening the inner end of a mainspring to the barrel arbor of a clockwork, characterized by the fact that the arbor has a surface of revolution which extends within the barrel, and by the fact that the inner end of the spring is cut in such a manner so as to be wound at least two'complete turns on the surface of revolution. The fastening of the spring to the arbor is effected by frictional resistance.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing shows, by way of example, two embodiments of the device in accordance with the invention.

FIGS. 1 and 2 are plan views of the inner end of the mainspring in each of its two embodiments.

FIGS. 3 and 4 are side elevations of a portion of the barrel arbor with the mainspring which is fastened to it in each of these embodiments, and

FIGS. 5 and 6 are sectional views along the lines VV and VI-VI of FIGS. 3 and 4, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the device, two embodiments of which will be described, the mainspring is fastened to the barrel arbor by friction. It has been found, as a matter of fact, that by imparting to the inner end of the mainspring a suitable shape which makes it possible to bring it into contact with the barrel arbor over a length equal to at least two turns, sufficient adherence to assure the connection is obtained.

Referring to FIG. 1, the inner end of the mainspring is cut in the form of a very elongated isosceles triangle the height of which is equal to twice the circumference of the central portion of the arbor. The apex of the isosceles triangle formed by the cut portion 1 of the spring 2 is truncated by a transverse edge 3 whose length is approximately equal to one-fifth the width of the spring 2. Furthermore, the triangular tip 1 is provided with an opening 4 which forms a geometrical figure approximately similar to that of the triangular tip I and the height of which is equal to one-half and the base to three-fifths of the height and the base of the tip 1. Under these conditions, as can be noted from FIG. 3, if the truncated triangular tip 1 is wound on itself around a cylindrical surface 5 which the arbor 6 has in its central portion, the end portion of the tip 1 fits into place in the opening 4 if the circumference of the surface 5 is equal to one-half the height of the triangular tip 1. The triangular tip is therefore in contact with the arbor along two complete turns. As it is applied against the arbor by elastic deformation, the frictional resistance which acts in the direction of the circumference of the arbor is multiplied by a very large factor, so that it is sufficient to assure the connection. The edge 7 which forms the base of the opening 4 rests against the edge 3 of the tip 1, as well as on the portion of the spring which is in the vicinity of the end of the opening 4. This edge could possibly be beveled. FIG. 5 shows in cross section how the edges of the opening 4 are applied against the arbor.

In the second embodiment (FIGS. 2, 4, 6), the spring 8 has a cut end portion 9 which constitutes a tongue whose width is approximately equal to one-third of the width of the solid portion of the spring. This tongue extends obliquely from one of the edges 13 of the spring 8 over a length which, measured along the longitudinal axis of the spring, is equal to twice the circumference of the cylindrical surface 10 of the arbor 11. The inclination of the tongue 9 to the longitudinal axis of the spring 8 is such that the extreme corner 12 of its inner edge extends in the extension of the other edge 14 of the spring. As can be noted from FIGS. 4 and 6, the tongue is wound helically in two adjacent turns around the surface 10, which also assures fastening by frictional resistance. In this case also the transverse edge 15 of the cutout could be beveled. As a variant, the tongue 9 could be narrower and longer than shown in FIG. 2 and be wound more than two turns around the arbor.

In this way there is obtained a fastening device which does not require any milling on the arbor of the barrel. The latter could have only lathe-turned surfaces intended for its pivoting in the frame of the movement and for the pivoting of the cover and drum of the barrel. Furthermore, as in the customary arbors, it will have a square portion for the fastening of the ratchet wheel. However, in other embodiments, the ratchet wheel could be fastened to the arbor by force-fitting or riveting, which would still further simplify the machining of the arbor. Possibly all the cylindrical surfaces for pivoting, for force-fitting of the ratchet wheel, and for the fastening of the mainspring could be of the same diameter, the arbor then being a cylindrical piece which can be obtained by cutting from bars of long length, the

cutting operations being reduced to their simplest form.

What is claimed is:

1. Means for fastening one end portion of a mainspring to a barrel arbor of a clockwork mechanism, wherein said arbor has a surface of revolution which extends within the barrel, said one end portion of said mainspring having a cut shape such that said one end portion is wound around said barrel arbor on said surface of revolution and makes contact with said barrel arbor for at least two complete turns to fasten said spring to said arbor by frictional resistance.

2. Fastening means according to claim 1, wherein said surface of revolution is cylindrical, and said one end portion of the spring is cut obliquely relative to the long axis of said spring.

3. Fastening means according to claim 2, wherein the cut portion of the mainspring comprises a tip having the shape of an isosceles triangle of a height approximately equal to twice the circumference of said surface of revolution,.having an opening of the same shape as said isosceles triangle shape which extends from the base of said triangle to approximately the center of the height of said triangle, the dimensions of said opening being substantially the same as those of the end portion of the triangular tip portion located between the apex of said opening and the end of said mainspring.

4. Fastening means according to claim 2, wherein the cut end portion of the mainspring has the shape of a tongue with parallel edges extending obliquely with re spect to the longitudinal axis of the spring, said cut end portion being wound in at least two adjacent turns on said surface of revolution.

5. Fastening means according to claim 4, wherein the length of said cut end portion, measured along the longitudinal axis of the spring, is approximately equal to twice the circumference of said surface of revolution, and wherein the width of said cut end portion is approximately equal to one-third the width of the uncut portion of the spring.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 2 3,834,154

DATED 3 September 10, 1974 INVENTORG) I Urs GIGER It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

The name of the Assignee is misspelled. The correct assignee ETA A.G. EBAUCHES-FABRIK of Grenchen (Soleure) Switzerland Signed and Sealed this second Day Of March 1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner uj'Parenrs and Trademarks 

1. Means for fastening one end portion of a mainspring to a barrel arbor of a clockwork mechanism, wherein said arbor has a surface of revolution which extends within the barrel, said one end portion of said mainspring having a cut shape such that said one end portion is wound around said barrel arbor on said surface of revolution and makes contact with said barrel arbor for at least two complete turns to fasten said spring to said arbor By frictional resistance.
 2. Fastening means according to claim 1, wherein said surface of revolution is cylindrical, and said one end portion of the spring is cut obliquely relative to the long axis of said spring.
 3. Fastening means according to claim 2, wherein the cut portion of the mainspring comprises a tip having the shape of an isosceles triangle of a height approximately equal to twice the circumference of said surface of revolution, having an opening of the same shape as said isosceles triangle shape which extends from the base of said triangle to approximately the center of the height of said triangle, the dimensions of said opening being substantially the same as those of the end portion of the triangular tip portion located between the apex of said opening and the end of said mainspring.
 4. Fastening means according to claim 2, wherein the cut end portion of the mainspring has the shape of a tongue with parallel edges extending obliquely with respect to the longitudinal axis of the spring, said cut end portion being wound in at least two adjacent turns on said surface of revolution.
 5. Fastening means according to claim 4, wherein the length of said cut end portion, measured along the longitudinal axis of the spring, is approximately equal to twice the circumference of said surface of revolution, and wherein the width of said cut end portion is approximately equal to one-third the width of the uncut portion of the spring. 